1. Field of the Invention
The present invention relates to a saveall apparatus for collecting water ejected from stock through a forming wire of a papermaking machine. More particularly, the present invention relates to a vacuum slot for a curved inverted vacuum box of a twin-wire former.
2. Information Disclosure Statement
In the papermaking art, stock is ejected from a headbox onto a moving fourdrinier wire such that water within the stock drains through the moving fourdrinier wire leaving a formed web on the surface of the wire.
Although the aforementioned forming procedure is generally effective for producing linerboard or a web of paper, if such a web is to be subsequently printed thereon, it is desirable that both surfaces of the resultant web should have uniform surface characteristics thereon. However, with the aforementioned drainage of water through a fourdrinier wire, the resultant web exhibits two-sidedness; that is, water is drained from the web in one direction only.
Consequently, more recently, so-called twin-wire formers have been built in which stock is ejected into a forming section defined between a pair of cooperating endless looped wires.
More particularly, water is removed from the stock during passage thereof through the forming section. Such water is squeezed through both wires, particularly when such wires extend around a curved surface guiding the cooperating wires. First, the pressure exerted by the wires on the sandwiched web causes water to be ejected from the formed web. Secondly, when the sandwiched web extends around a curved guide surface, water is thrown centrifugally through the outermost wire during passage around the curve so that a gradual dewatering from both sides of the resultant web can be achieved. Typical of such twin-wire formers is the Horizontal Bel Baie twin-wire former manufactured and sold by Beloit Corporation. The Horizontal Bel Baie is described in U.S. Pat. No. 4,894,120 to North.
Another type of twin-wire former is the BEL BOND former which is a former designed as a retrofit to an existing fourdrinier wire. BEL BOND is a registered trademark of Beloit Corporation. The BEL BOND includes a looped top wire which cooperates with the existing fourdrinier wire and includes a curved inverted vacuum box within the loop of the upper wire.
The curved inverted vacuum box (CIVB) is positioned within the endless loop of the upper wire in order to collect water ejected from the stock through the upper forming wire.
The CIVB essentially includes a box fabricated from stainless steel or the like with the box defining an enclosure connected to a source of partial vacuum. The box includes a base having a convex curved surface for guiding the upper wire so that a portion of water is removed from the formed web downwardly through the fourdrinier wire during movement of the wires over such curved surface.
A vacuum slot is provided at the upstream end of the box for collecting water previously ejected from the stock through the upper wire upstream relative to the CIVB. The vacuum slot is connected to the enclosure such that water is drawn through the vacuum slot up and into the curved inverted vacuum box.
In the prior art vacuum slots, a stationary throat wall, is rigidly secured to the upstream end of the box for initially guiding the top wire under the CIVB.
A moveable throat wall having a first and a second end is pivotally secured at the second end thereof to the box such that controlled pivotal movement of the moveable throat wall varies the cross-sectional area of a vacuum slot defined between the moveable throat wall and the stationary throat wall.
More specifically, a manually operated jack pivotally connected to and extending between the first end of the moveable throat wall and the box enables manual movement of the moveable wall relative to the throat wall for adjusting the flow of water through the vacuum slot.
However, the aforementioned arrangement inherently generates various problems in use thereof. For example, a typical curved inverted vacuum box weighs in the region of 30 tons, and the moveable throat wall thereof may have a width in the region of 40 feet. Therefore, accurate adjustment of the moveable wall relative to the stationary wall is relatively difficult.
Furthermore, with the aforementioned arrangement, there exists a tendency for the moveable wall to inadvertently strike the stationary throat wall upon closure of the vacuum slot.
The present invention provides means for accurately adjusting the position of a moveable throat wall relative to a stationary throat wall of a vacuum slot while preventing damage to the stationary wall by inadvertent striking of the stationary wall by the moveable throat wall.
Therefore, it is a primary objective of the present invention to provide a saveall apparatus which overcomes the aforementioned disadvantages of the prior art proposals and to provide an apparatus which makes a considerable contribution to the art of web formation.
Another objective of the present invention is the provision of a saveall apparatus which includes a throat wall disposed in a first plane and a moveable throat wall disposed in a second plane such that when the moveable throat wall is moved relative to the throat wall, an angle defined between the planes remains constant so that accurate adjustment of the position of the moveable throat wall relative to the throat wall is permitted.
Another object of the present invention is the provision of a saveall apparatus in which striking of the throat wall by the moveable throat wall is prevented.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter, taken in conjunction with the annexed drawings.